In the method known from DE 10 2004 014 653 A, in the recovery phase, air from the respective blow mold is first fed into a volume allocated to a blow stage higher than the preblow stage, and only subsequently, the volume allocated to the preblow stage is fed from this volume, the pressure being controlled to the pressure for the preblow stage. The higher blow stage following the preblow stage ranges up to a relatively high pressure of about 30 bar, while the highest blow stage ranges up to a very high pressure of about 40 bar. The air from the respective blow mold is only fed into the volume in the highest pressure stage of the recovery phase up to a pressure approximately corresponding to the pressure of the blow stage following the preblow stage, while an operating air storage is fed in the next pressure stage of the recovery phase. Apart from the fact that the high pressure of the highest blow stage requires an undesired high energy demand, the pressure usable for the preblow stage which is secondarily fed is inappropriately low. As during the blowing process, pressure variations inevitably occur in the volume allocated to the preblow stage due to the feeds and the preblow stages, and as the pressure potential in the volume allocated to the preblow stage is low, there are extremely undesired fluctuations in the preblow stage. The preblow stage already definitely determines the material distribution in the preform, possibly depending on the temperature profile, which hardly changes any more in the following blow stages. The mentioned fluctuations then result in an unsatisfactory constancy of the volumes of the blow-molded containers and/or in non-uniform individual segment weights of the containers. With an only low pressure potential in the volume allocated to the preblow stage, the air flow can furthermore become subcritical during the preblow stage. Thus, the preblow stage volume flow rate cannot be adjusted to be exactly reproducible due to the pressure variations in the volume allocated to the preblow stage arising by the feeds during the recovery phase. As a result, a constant quality of the blow-molded containers cannot be ensured due to the fluctuations occurring in the preblow stage.
In a method known from EP 1 9 22 206 A, in the recovery phase, a volume common to several consumers is first primarily fed by building up a relatively low pressure of about 17 bar therein, and the volume allocated to the preblow stage is only fed secondarily, in which compulsorily only a very low pressure potential for the preblow stage is formed, resulting in the above-mentioned disadvantages. In this known method, too, the blow stage following the preblow stage is carried out up to a relatively high pressure of about 18 bar, while in the highest blow stage, operation is effected with a pressure of up to 40 bar requiring an extremely high energy demand.
In a method known from DE 10 2007 015 105 A with a pressure build-up in the manner of a cascade, the lowest pressure stage in the relief of the blow mold is used for the pressure build-up in the volume for the preblow stage in the recovery phase, which can lead to a relatively low pressure potential in the volume allocated to the preblow stage involving the above-mentioned disadvantages. If the preblow stage is embodied as first pressure build-up step of the final blow stage, the preblow stage is integrated in the cascade-like pressure build-up of the final blow stage. Concretely, the preblow pressure is built up from an individual storage, and in the process, the proportion of the compressed gas from the blow mold originating from the lowest relief stage is used for filling up the preblow pressure. If, however, the preblow stage is embodied, as the final blow stage, with several pressure build-up steps each from several separate storages, the lowest pressure relief steps of the final blow stage are used for the pressure build up of the preblow stage.